Wireless communication systems, also known as Public Land Mobile Networks (PLMN) are well known and widely deployed. A variety of protocols are in use, such as GSM, CDMA 2000, WCDMA, UMTS, and the like. These systems are operated at different frequencies by different service providers, depending on the spectrum allocated and made available by the governments of the countries in which they are deployed. In particular, many systems utilize Frequency Division Duplex (FDD), whereby downlink traffic from a network to User Equipment (UE) is transmitted on carriers that are spaced apart in frequency from uplink traffic from UE to the network. Other systems utilize Time Division Duplex (TDD), and carry both uplink and downlink transmissions in one frequency band. Frequency bands that are utilized in one geographical area may or may not be the same frequencies used in other geographical areas. For example, while most of Europe has service providers offering GMS in bands at 900 and 1800 MHz and UMTS at 2100 MHz, service providers in both Sweden and Norway also provided a CDMA 2000 system at 450 MHz.
Modern mobile UE often include frequency-agile transceivers, and can operate in two or more different PLMNs operating at different frequencies. On power-up, for example, these UE scan all of the frequencies in which they can operate, to locate an operative PLMN cell and register for wireless communication services. The UE may operate only within the “found” frequencies, so long as the user does not move out of the current geographical area. To detect such movement, and for other reasons, the UE periodically engages in a full linear search of all supported frequencies. This is to detect movement into a different geographical area, and also to locate a preferred or prioritized PLMN (for example, one having an economic arrangement with the user's home PLMN that reduces the cost of the preferred PLMN over other available systems), or to locate a system that provides additional services (e.g., dedicated packet data services, audio/video content broadcasts, and the like).
A full frequency search consumes power, as the transceiver circuits must change their operating characteristics. Since most mobile UE are battery powered, conserving power consumption is an important consideration, to provide a reasonable useful life between recharges. Accordingly, full searches of the mobile UE's supported spectrum are preferably infrequent from the viewpoint of power management. However, a longer delay between such frequency band searches prolongs the time required for the mobile UE to detect a new cell when the UE leaves the current geographical area and moves into another geographical area where other frequency bands are utilized. It would therefore be beneficial for the mobile UE to detect its movement into another geographical area, to trigger a frequency search sooner than the next scheduled routine frequency search.